Project Summary Nearly one third of births in 2017 were by Cesarean section, a rate that expects widely agree is higher than necessary and results in excess costs and health complications (Hamilton et al., 2018; Spong et al., 2012). Public and private payers have begun introducing payment reforms designed to lower costs and improve health outcomes. Although bundled payments hold promise for addressing high Cesarean section rates and other problems in perinatal care, little is known about their effects. This study will examine the introduction of perinatal bundles by Medicaid in three states: Arkansas, Ohio and Tennessee. Existing research on an all-payer perinatal bundled payment in Arkansas found moderately reduced spending resulting from lower input prices, but no changes in practice patterns or health outcomes (Carroll et al., 2018). This study will build on this existing research by examining outcomes in Arkansas using a new data source, and by estimating the physician responses to more recent perinatal bundles in Ohio and Tennessee. Unlike the bundle in Arkansas, the payment reforms in Ohio and Tennessee targeted a single population, Medicaid patients, and included quality hurdles physicians must meet to be eligible for shared savings. This study will explore direct effects of the new payment policy related to practice patterns, costs and health outcomes and any indirect effects in the form of lower access or risk selection of patients.